Inadequate half-lives of therapeutics often necessitate their administration at high frequencies and/or higher doses, or the use of sustained release formulations, in order to maintain serum levels necessary for therapeutic effects. However, this is often associated with negative side effects. One strategy for overcoming inadequate half-lives is to fuse the therapeutic to a half-life-extending polypeptide. Yet, while the extension of half-life may be beneficial, an overly stabilized therapeutic may also lead to negative side effects. Accordingly, the ability to fine tune the half-lives of therapeutics can be beneficial. This application provides compounds that fine tune the serum half-lives of various therapeutics and methods for generating the same.